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ON MONDAY this week, astronomers at the European Space Agency succeeded
in their attempts to resuscitate Europe’s damaged Giotto spacecraft, originally
put in orbit to examine Halley’s Comet.

Å®ÉúСÊÓƵs working at NASA’s Deep Space Network sent out the signals
and Giotto’s answer came back loud and clear. The ESA can now send the spacecraft
on an extra mission to examine another comet, Grigg Skjellerup.

The agency did not expect Giotto to survive the trauma of passing through
the dusty tail of Halley’s Comet undamaged in March 1986, but researchers
found that the spacecraft still responded to messages from Earth. This gave
the astronomers an opportunity to obtain further data by extending Giotto’s
mission at relatively low cost.

They redirected Giotto so that in June, it will pass close to the Earth,
enabling the team to position it so that the Earth’s gravitational field
can send it off in a new orbit. Giotto should now meet up with the comet,
Grigg Skjellerup, in July 1992.

David Dale, head of science projects at the ESA’s research centre in
Noordwijk, in the Netherlands, said that he had had no idea whether the
attempt to reactivate Giotto would succeed. ‘Giotto was a beautiful piece
of engineering work. It proved extremely reliable, so as long as there has
been no catastrophic damage I can see no reason why it shouldn’t work,’
he said last week before the attempt to redirect Giotto.

The team knows that some of the instruments on board Giotto are damaged
– its camera has lost the light shield that deflects the intense rays of
the Sun. Another device, which helps astronomers to pinpoint the spacecraft,
is also broken. But Giotto is now spinning on an axis slightly askew from
its original, so the astronomers can calculate its position by examining
the wobble this creates in signals from Giotto.

The team from the ESA, working out of the agency’s Space Operations
Centre in Darmstadt, West Germany, must now establish whether the software
on board still functions. They sought to bombard the spacecraft with powerful
signals from NASA’s Deep Space Network. Giotto was spinning at an angle
which meant that even if it responded, its antenna would send back a reply
that was no more than a whisper. But now the astronomers have made contact
they will be able to command Giotto to turn around. This manoeuvre is crucial
if future signals are to be strong enough to bring back meaningful data.

Not all comets behave alike. Grigg Skjellerup is relatively old, which
in astronomical terms means that it has spent a significant portion of its
lifetime in the inner reaches of the solar system. The comet should reveal
interesting data about the chemical structure of its tail and its nucleus.
Giotto still has sufficient fuel on board to fly back to a position close
to Earth and, at a cost of $15 to $20 million.